1 of 7 SPECIFICATIONS FOR POT / POT cum PTFE and ELASTOMERIC BEARINGS

Transcription

1 1 of 7 SPECIFICATIONS FOR POT / POT cum PTFE and ELASTOMERIC BEARINGS 1 BEARING 1.1 GENERAL This work shall consist of design, supply and fixing in position of bearings for bridge girders in accordance with details shown on drawings and to the requirements of these specifications, codes and standards quoted therein, and as directed by Engineer. 1.2 Bearing plates, assemblies and other expansion or fixed devices shall be constructed in accordance with details shown on drawings. When bearing assemblies or plates are shown on drawings to be placed (not embedded) directly on concrete, the concrete bearing area shall be constructed leveled and finished by grinding, if required. 1.3 It shall be ensured that the bearings are set truly level and in exact position as indicated on drawings so as to have full and even bearings on the seats. This shall be checked with spirit level in both directions. Thin epoxy mortar pads (not exceeding 5 mm) may be made to meet with this requirement. It shall be ensured that the bottoms of grinders to be received on the bearings are plain at the location of these bearings and care shall be taken that the bearings are not displaced while placing the girders. 1.4 When Elastomeric Bearing pads are to be provided, the concrete surfaces on which pads are to be placed shall be wood float finished to a level plane, which shall not vary by more than 1.5 mm from a straight edge placed in any direction across the area. A. POT BEARING A.1 Material specifications of Pot Bearing The material such as PTFE lubrication, confined elastomer, stainless steel and internal seal shall conform to the requirements of IRC: 83 (Part III) The Pot base, saddle & top plate shall be of Cast steel conforming to the properties of IS: 1030 with optional 0.2 % to 0.5 % traces of copper to enhance the corrosion resistant properties. Painting on non-working surfaces of bearings shall be done using High Build Zinc rich Epoxy primer and Paint (two coats each) to give a total dry film thickness of 150 microns. The mating surface of Piston and cylinder shall be hardened to 350 BHN (Min.). Guides of sliding pot bearing and all accessories shall be the responsibility of the Contractor and got approved from the Client s Representative.

2 A.2 Permissible stress in steel component of Pot bearing 2 of 7 The entire design requirement for Pot bearing as specified in IRC: 83 (Part III) has to be fulfilled with following points duly taken care of: (a) No increase in permissible stresses in material of any steel component is permitted in seismic condition. A.3 Permissible bearing stresses in concrete The allowable bearing stresses in concrete shall be calculated considering a maximum angle of dispersion of 63 0 (dispersion ratio of 2:1) and the maximum area for dispersion available. (a) Increase of 25% in permissible bearing stress between concrete and bearing is permitted in seismic condition. A.4 Anchor sleeve All the parts of bearings such as anchor sleeves embedded in concrete shall be designed taking account of difference in elasticity of steel of sleeves and concrete. The effect of shifting of center of rotation of sleeve should also be taken into account. A.5 The contractor shall furnish along with tender documents in technical bid, the name of the manufacturer of bearings, his qualifications with all details including proof of satisfactory performance, certification and testing facilities of the bearing he proposes to use. Products of manufacturers prequalified by MORT&H shall only be used. The design, drawings and detailed method statements for installation and replaceability of the bearings shall be checked and certified by the manufacturer before submitting to the Engineer for approval. A.6 Pot bearings shall be measured in numbers, Pin Pot bearing, Longitudinal Guide Pot bearing, Transverse Guide Bearing and Free Pot Bearing shall be counted separately, according to their capacities. The rate shall include the cost of supplying and providing supervision for fixing the bearing in position. The cost shall also include the cost of samples and their testing as required conforming to the specifications. A.7 Testing of Pot Bearing A.7.1 A.7.2 All Bearings shall be checked for surface finish or any other discernible superficial defects. All the bearings shall be checked for overall dimensions as per the Manufacturing tolerances specified in the codes and the specifications.

3 A.7.3 A.7.4 A.7.5 A of 7 One Bearing selected at random from each lot of 25 Nos. Bearings shall be load tested to 1.25 times the maximum design vertical load capacity as shown in the drawings for a minimum period of 30 minutes. Few Bearings subjected to a minimum of one bearing per Lot selected randomly shall be tested for permissible rotation. A pair of movable Bearings (Free Float and Slide Guide Types) selected at random shall be tested in order to determine the co-efficient of friction "µ" which shall not exceed 0.03 at the maximum vertical design load. For Bearings required to resist horizontal forces (Fixed and Slide Guide Types), one Bearing selected at random from each lot of 25 Nos. shall be subjected to combined Vertical and Horizontal Load Test to 1.10 times of the respective maximum design loads and forces. The bearing will be visually examined both during the test and upon disassembly after the test. Any resultant visual defects, such as extruded or deformed elastomer or PTFE, damaged seals, or cracked steel, shall be cause for rejection. During the test, the steel bearing and steel piston shall maintain continuous and uniform contact for the duration of the test. Any observed lift-off will be cause for rejection. IMP: It is necessary that all manufacturers of the Bearings shall have in - house facilities for carrying out all the Tests required as per relevant Codes and Specifications. A.8 Sampling and Testing A.8.1 Lot size Sampling testing and acceptance considerations will be made on a lot basis. A lot shall be defined as those bearings presented for inspection at a specific time or date. A lot shall further defined as the smallest number of bearings as determined by the following criteria. (a) A lot shall not exceed a single contract or project quantity. (b) A lot shall not exceed 25 bearings. (c) A lot shall consist of those bearing of the same type regardless of load capacity. Bearing types shall be fixed or expansion bearings types. Guided and non-guided expansion bearing shall be considered a single type. A.8.2 Sampling and testing requirements A minimum of thirty (30) days shall be allowed for inspection, sampling and testing of production bearings and component materials.

4 4 of 7 All exterior surfaces of production bearings shall be smooth and free from irregularities or protrusions that might interfere with testing procedures. However, the non working surfaces of the Bearing can be left as cast. The manufacturer shall select, at random, the required sample bearing(s) from complete lots of bearings for testing by the manufacturer. He shall complete the required testing and determine compliance with this specification before submitting the lot(s) for inspection, sampling, and acceptance consideration. The Engineer shall select, at random, the required sample bearing(s) from completed lots of bearings. Necessary test certificates for all raw materials shall be furnished by manufacturer. Test specified in the relevant codes and specifications for steel material shall be performed. Castings shall be ultrasonically tested by approved testing agency. A.9 Fabrication Details The contractor shall provide the Engineer with written notification thirty (30) days prior to the start of bearing fabrication. This notification shall include all of the information shown on the Shop Drawings which are required as explained in subsequent section. The finish of the mould used to produce the elastomeric rotational element shall conform to good machine shop practice. All steel surfaces exposed to the atmosphere, except stainless steel surfaces and metal surfaces to be embedded, shall be shop painted in accordance with the contract plans. Prior to painting, the exposed steel surface shall be cleaned in accordance with the recommendations of the coating s manufacturer. Metal surfaces to be welded shall be given a coat of clear lacquer, or other protective coating approved by the Engineer, if the time of exposure before welding takes place is to exceed three months, the coating shall be removed at the time of welding. No painting will be done to these surfaces prior to the completion for welding. Stainless steel shall be attached to its steel substrate with a continuous fillet weld all along its periphery. The steel piston and the steel pot shall each be machined from a solid piece of cast steel. The outside diameter of the piston shall be no more less than 1.5 mm than the inside diameter of the pot at the interface level of the piston and elastomeric rotational element. The sides of the piston shall be beveled to facilitate rotation. Except as noted all bearing surface of steel plates shall be finished or machined flat in accordance with tolerance written below:-

5 Tolerances:- 5 of 7 Manufacture tolerance shall be as per IRC: 83 (Part III) All the measurements are to be taken using pre-calibrated dial height gauges, vernier calipers, surface finish measurement instrument etc. that has to be arrange by the manufacturer at the workshop. Every bearing shall have the identification plate showing manufacturing date, capacity, and individual bearing number and shall be punched on a side that will be visible after erection. After assembly, bearing components shall be held together with steel strapping, or other means, to prevent disassembly until the time of installation. Packaging shall be adequate to prevent damage from impact as well as from dust and moisture contamination during transportation and storage. A.10 Shop Drawings Along with detailed design of different types of bearing, Shop Drawings shall be submitted. The Shop Drawings shall contain the following information, which is necessary for proper design and detailing of the bearings. Quantity, type (Fixed, Guided Expansion, Non - Guided Expansion), location and orientation of all bearing units. A table containing maximum and minimum Vertical Loads, Horizontal forces and translation capacity of the Bearings. Table showing Bearing performance characteristics, stresses in concrete interfaces at Top and Bottom and also in crucial components inside the Bearing itself like the Elastomer and PTFE. The paining system to be used on the steel components to guard against corrosion. Any special consideration such as earthquake requirements, uplift details, or temporary attachments. Installation scheme of pot bearings. The contractor shall submit detailed Methodology of Installation in conformance with the applicable requirements.

6 6 of 7 B. ELASTOMERIC BEARINGS The term bearing in case refers to an Elastomeric Bearings consisting of one or more internal layers of elastomer bond to internal steel laminates by the process of vulcanization. The bearing shall cater for translation and / or rotation of the superstructure by elastic deformation. B.1 Raw Material Chloroprene (CR) Rubber shall be used in the manufacture of the bearing. The use of Natural Rubber shall not be allowed for use. Grades of raw elastomer of proven use in elastomeric bearings, with low crystallization rates and adequate shelf life (eg. Neoprene with low crystallization rates and adequate shelf life (eg. Neoprene WRT, Bayprene 110 Skyprene B- and Denka S-40V) shall be used. No reclaimed rubber or vulcanized wastes shall be used. The raw elastomer content of the compound shall not be lower than 60 percent by its weight. The ash content shall not exceed 5 percent (as per tests conducted in accordance with ASTM D-297, sub-section 10). EPDM and other similar candidate elastomers for bridge bearing use shall not be permitted. B.2 Properties The elastomer shall conform to the properties specified in IRC: 83 (Part II) B.3 Fabrication and Tolerance Fabrication and Dimensional requirement shall satisfy the requirements of the relevant codes and specifications and in general shall be complying to the IRC: 83 (Part II) Sampling, testing and acceptance consideration will be made on a lot basis. A lot shall be defined as those bearings presented for inspection at a specific time or date. A lot shall be further defined as the smallest number of bearings as determined by the following criteria (a) A lot shall not exceed a single contract or project quantity. (b) A lot shall not exceed 24 bearings. (c) A lot shall consist of those bearing of the same type regardless of load capacity.

7 7 of 7 Accepting and testing requirements shall also conform to the specifications laid down in the contract plans and as referred in IRC: 83 (Part II) In addition to tests mentioned above, all bearings shall be also weight actually and compared with the theoretical weight. All bearings shall carry a warrantee in an approved format for the period mentioned in the Contract / Tender Documents. The contractor shall be responsible for immediate repair or replacement of the bearings in case of failure / distress to the satisfaction of the owner at no extra cost to the owner within the warrantee period. IMP: It is necessary that all manufacturers of the Bearings shall have in - house facilities for carrying out all the Tests required as per relevant Codes and Specifications. B.4 Design The design of Elastomeric Bearings shall be as per the guidelines laid down in the IRC: 83 (Part II) The design, drawings and detailed method statements for installation and replaceability of the bearings shall be checked and certified by the manufacturer before submitting to the Engineer for approval. B.5 Storage and Handling Each Elastomeric Bearings shall be clearly labeled or marked. The bearing shall be wrapped in cover. They shall be packed in timber crates with suitable arrangement to prevent movement and to protect comers and edges. Care shall be taken to avoid mechanical damage, contamination with oil, grease and weather to the bearings during transport and handling prior to and during installation. B.6 Installation Installation procedure shall conform to the detailed methodology of Installation submitted by the Manufacturer. B.7 Measurement Measurement shall be made in cu. cm. correct to two places of decimals. All linear dimensions required to arrive at volume of elastomer shall be measured correct to a mm.